1. Technical Field
Embodiments of the present invention relate generally to wireless digital communication systems and methods and, more specifically, to a system and method for optimal listen before transmit in wireless communications.
2. Description of the Related Art
A conventional wireless digital communication system includes at least two nodes, each incorporating a digital radio transceiver. Each node may transmit a data payload to another node via the digital radio transceiver. Certain wireless digital communications systems are required to implement a listen before transmit protocol, whereby a node must listen for energy on a selected channel prior to transmitting on the selected channel. One goal of a listen before transmit protocol is to avoid interference among nodes that are attempting to transmit on the same channel. In many normal operating scenarios, a typical listen before transmit protocol provides adequate statistical arbitration to enable multiple nodes that are competing to transmit on a given channel to eventually transmit data payloads on the channel. In such scenarios, each node is well-behaved and yields the channel to other nodes, which are then able to transmit respective data payloads.
Different types of nodes may share a common channel, but may implement different, unfamiliar modulation and coding schemes, introducing the possibility of a transmission from one node being indistinguishable from radio frequency interference (RFI) to another node. To overcome this ambiguity, listen before transmit protocols typically characterize channel occupancy based only on measured energy within the channel. Unfortunately, this definition for channel occupancy allows an arbitrary RFI source to disable a node from ever transmitting on the channel. For example, certain electromechanical machines, such as commutating electric motors, may emit sufficient RFI energy within the channel to prevent a nearby node from ever transmitting within the channel.
In certain common scenarios, a target node is located close to a localized RFI source, while a source node that is attempting to communicate with the target node is located a significant distance from any localized RFI source. The source node may transmit a data payload to the target node via the selected channel and wait for an acknowledgement on the channel from the target node before proceeding. Even if the target node successfully receives the data payload, localized energy from the RFI source within the channel may prevent the target node from transmitting an acknowledgment receipt of the data payload. In such scenarios, the localized RFI source may render conventional listen before transmit protocols inoperable.
As the foregoing illustrates, what is needed in the art is a more robust technique for implementing a listen before transmit protocol in wireless digital communication systems.